Bioanalysis

Cells in Paper

Cell cultures in stacked, paper-supported gels offer a flexible approach to study cell responses against 3D molecular gradients of oxygen, nutrients, chemicals, or biological molecules. A schematic for the Cells-in-Gels-in-Paper (CiGiP) platform for culturing mammalian cells is given in Figure 1. This approach can be useful to mimic tissue- and organ-level functions in vitro and in vivo (Figure 2).

Permeating a suspension of cells in hydrogels into the paper matrix creates thin 3D tissues in which the growth of cells is not limited by mass transport of oxygen or nutrients. Stacking and de-stacking layers of paper impregnated with suspensions of cells in hydrogels make it possible to control oxygen and nutrient gradients in three dimensions (3D), and to analyze molecular and genetic responses. Stacking assembles the tissue construct whereas de-stacking disassembles it, and permits its analysis.

Using these systems, we study the role of molecular gradients on drug and radiation sensitivity of cancer cells in 3D tumors (Figures 3 and 4), high-throughput testing of the effect of soluble compounds, cardiac ischemia-reperfusion injury, mineralization in 3D constructs, and the formation and control of bacterial communities (biofilms) in 3D.

Thin polymer meshes can also be used as similar 3D culture systems. An example for the Cells-in-Gels-in-Mesh (CiGiM) that uses stacked sheets of polymer-based mesh is given in Figure 5. These constructs support cells embedded in gels to form tissue-like structures.

We project that paper, which is widely available in any laboratory, and simple to use, will become the foundation for the next generation of screening and bioassay platforms that use 3D tissues as assay targets.